U.S. patent number 4,928,750 [Application Number 07/257,566] was granted by the patent office on 1990-05-29 for vav valve with pwm hot water coil.
This patent grant is currently assigned to American Standard Inc.. Invention is credited to Mark E. Nurczyk.
United States Patent |
4,928,750 |
Nurczyk |
May 29, 1990 |
**Please see images for:
( Certificate of Correction ) ** |
VaV valve with PWM hot water coil
Abstract
A refrigeration system for temperature conditioning several
comfort zones includes several VAV (variable air volume) valves
each having a hot water coil conveying water whose flow rate is
regulated by a PWM (pulse-width modulated) solenoid valve. Each VAV
valve is connected to a supply air duct conveying cool supply air.
When a zone's temperature is above a set point temperature, the
opening of the VAV valve is modulated to meet the cooling demand,
and the water coil is shut off. When a zone's temperature is below
the set point, the VAV valve is opened to provide a predetermined
constant airflow rate and the hot water coil's solenoid valve is
cycled open and closed in a pulse-width modulated manner to meet
the heating demand.
Inventors: |
Nurczyk; Mark E. (Eastman,
WI) |
Assignee: |
American Standard Inc. (New
York, NY)
|
Family
ID: |
22976806 |
Appl.
No.: |
07/257,566 |
Filed: |
October 14, 1988 |
Current U.S.
Class: |
165/216; 165/217;
236/1B; 236/1C; 236/46F; 236/49.3; 251/129.05 |
Current CPC
Class: |
F24D
19/1084 (20130101); F24F 3/06 (20130101); F24F
11/053 (20130101); F24F 11/06 (20130101) |
Current International
Class: |
F24D
19/10 (20060101); F24D 19/00 (20060101); F24F
11/04 (20060101); F24F 11/053 (20060101); F24F
11/06 (20060101); F24F 3/06 (20060101); F24F
011/053 (); F24F 011/06 (); F25B 029/00 () |
Field of
Search: |
;165/16,22,26,27,28,30,39 ;62/90,173 ;236/1B,1C,46F,49.3
;251/129.05 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2222616 |
|
Oct 1974 |
|
FR |
|
2329012 |
|
May 1977 |
|
FR |
|
Primary Examiner: Ford; John
Attorney, Agent or Firm: Beres; William J. Harter; Robert J.
O'Driscoll; William
Claims
I claim:
1. A VAV valve assembly comprising:
a temperature sensor associated with a comfort zone;
a valve body adapted to be connected in series with a supply air
duct conveying airflow to said comfort zone, said airflow being at
a temperature below a zone temperature of said comfort zone as
sensed by said temperature sensor;
a moveable closing member disposed inside said valve body and
having a variable position that varies the flow rate of said
airflow;
control means for generating at least one command signal in
response to said temperature sensor;
drive means coupled to said closing member for varying said
variable position of said closing member in response to said at
least one command signal, whereby the flow rate of said airflow
varies as a function of zone temperature;
fan means connected to said valve body for drawing ambient air into
said valve body and discharging said ambient air into said comfort
zone, said valve body being at a higher elevation than said comfort
zone so that said ambient air tends to be warmer than said comfort
zone;
a coil connected to said valve body and adapted to convey a fluid
through said valve body to heat said airflow and said ambient air
to a temperature greater than said zone temperature; and
a solenoid valve connected in series with said coil to control the
flow of said fluid through said coil in response to said at least
one command signal such that said solenoid valve remains
substantially closed when said closing member is open beyond a
predetermined position and such that said solenoid valve cycles
between fully open and closed in a pulse-width modulated manner
with a duty cycle that varies in response to said at least one
command signal when said closing member is open no further than
said predetermined position, said duty cycle having a predetermined
maximum closed-period to avoid uncomfortable temperature
fluctuations of said airflow.
2. The VAV assembly as recited in claim 1, further comprising a
flow sensor means for providing said control means with a flow rate
feedback signal indicating the actual rate of airflow through said
VAV valve, said at least one command signal varying in response to
said flow rate feedback signal.
3. The VAV valve assembly as recited in claim 1, wherein said
solenoid valve cycles at a variable frequency that increases as
said duty cycle decreases.
4. The VAV valve assembly as recited in claim 1, wherein said duty
cycle varies as a function of an error between said zone
temperature and a predetermined temperature set point and further
varies as a function of the time at which said error exists.
5. The VAV valve assembly as recited in claim 1, further comprising
a check valve means connected to said valve body for ensuring
substantially unidirectional flow of said ambient air into said
valve body.
6. The VAV valve assembly as recited in claim 1, wherein said
solenoid valve is downstream of said coil with respect to said
fluid being conveyed therethrough.
7. A system for conditioning a plurality of comfort zones
comprising:
a refrigerant compressor, a condenser, an expansion device, an
evaporator, and an evaporator fan all of which cooperate to
function as a source of supply airflow;
a plurality of temperature sensor means with a temperature sensor
means associated with each of said plurality of comfort zones and
each having a selectable set point temperature;
flow sensor means associated with each of said VAV valves for
generating a flow rate feedback signal indicating the actual rate
of airflow through each of said VAV valves;
at least one control means generating, in response to said flow
rate feedback signal and said temperature sensor means, at least
one command signal;
supply air duct network means connecting each of said comfort zones
to said source of supply airflow to convey said supply airflow from
said source to each of said zones, said supply airflow being cooled
by said evaporator to a temperature below a zone temperature as
measured by at least one of said temperature sensor means;
a plurality of VAV valves with a VAV valve associated with each of
said plurality of comfort zones, said VAV valves being connected to
said supply air duct network means for regulating said supply
airflow to each of said zones in response to said at least one
command signal;
fan means and check valve means connected to at least one VAV valve
for drawing ambient air into said one VAV valve and discharging
said ambient air into at least one comfort zone, said one VAV valve
being at a higher elevation than said one comfort zone so that said
ambient air tends to be warmer than said one comfort zone;
a plurality of coils with a coil associated with each of said VAV
valves, each of said coils being adapted to convey a fluid to heat
said supply airflow and said ambient air to a temperature greater
than said zone temperature;
a plurality of solenoid valves with a solenoid valve associated
with each of said plurality of coils to control the flow of said
fluid through said coil in response to at least one command signal
so that for each zone and its associated VAV valve, associated
temperature sensor means, associated coil, and associated solenoid
valve, when a zone temperature is above said set point temperature
of said associated temperature sensor means, said associated
solenoid valve remains substantially closed and the opening of said
associated VAV valve varies to regulate the flow rate of said
airflow as a function of zone temperature, and when a zone
temperature is below said set point temperature of said associated
temperature sensor means, said associated solenoid valve cycles
between fully open and closed in a pulse-width modulated manner
with a duty cycle that varies as a function of an error between
said zone temperature and said selectable set point temperature and
further varies as a function of the time at which said error exists
while said associated VAV valve opens to provide a substantially
constant flow rate of said supply airflow, said duty cycle having a
predetermined maximum closed-period to avoid uncomfortable
temperature fluctuations of said airflow.
8. The system as recited in claim 7, wherein each of said solenoid
valves cycles at a variable frequency that increases as said zone
temperature increases.
9. The system as recited in claim 7, wherein said solenoid valves
are downstream of said coils with respect to said fluid being
conveyed therethrough.
10. A method of temperature conditioning a comfort zone comprising
the steps of:
drawing air from said comfort zone;
cooling said air to produce temperature conditioned supply air;
conveying said supply air back to said comfort zone by way of a VAV
valve;
sensing the flow rate of said supply air passing through said VAV
valve;
setting a desired set point temperature of said comfort zone;
sensing a zone temperature of said comfort zone;
when said zone temperature is above said set point temperature,
varying the degree of opening of said VAV valve as a function of
said temperature of said comfort zone, said set point temperature,
and the flow rate of said supply air; and
when said zone temperature is below said set point temperature,
i. positioning said VAV valve to provide a substantially constant
flow rate of said supply air,
ii. drawing ambient air from above said comfort zone into said VAV
valve.
iii. heating said supply air and said ambient air to a temperature
greater than said zone temperature using a coil conveying a heated
fluid through said VAV valve, and
iv. regulating the average flow rate of said fluid by open and
close cycling of a solenoid valve connected to said coil with an
open period of said solenoid valve relative to a closed period of
said solenoid valve increasing as said zone temperature decreases,
said closed period being of a predetermined maximum closed-period
to avoid uncomfortable temperature fluctuations of said supply
air.
11. The method as recited in claim 10, wherein the cycling of said
solenoid valve is at a variable frequency.
Description
TECHNICAL FIELD
This invention generally pertains to the temperature conditioning
of a plurality of comfort zones using a plurality of variable air
volume valves and more specifically pertains to reheating a cool
supply airflow to meet a heating demand.
BACKGROUND OF THE INVENTION
Many refrigeration systems can provide a variable supply of cooled
air to cool multi-zone buildings. The amount of cooled air conveyed
to each zone is often regulated by valves to meet each zone's
cooling demand. Valves used for such a purpose are commonly
referred to in the industry as VAV (variable air volume)
valves.
A problem exists when one or just a few zones require heating while
the rest of the zones still require cooling. Simply shutting off
the cool supply air to these few zones is an unsatisfactory
solution to the problem, because each zone requires at least some
ventilation. Providing each zone with an additional supply air duct
for heating is another possible solution, but one which is very
expensive, especially when retrofitting an existing structure.
SUMMARY OF THE INVENTION
To avoid the problems associated with present VAV systems, it is an
object of the invention to independently temperature condition a
plurality of comfort zones by heating some zones while cooling
others by selectively reheating portions of a common supply of cool
air prior to conveying the supply air to the zones.
Another object of the invention is to coordinate the positioning of
a VAV valve and the cycling of a solenoid valve.
Another object of the invention is to coordinate the positioning of
a VAV valve and the cycling of a solenoid valve in response to a
temperature sensor and an airflow sensor.
Yet another object of the invention is to regulate the average flow
rate of a hot fluid using a simple open-closed control scheme.
A further object of the invention is to vary the duty cycle of a
PWM solenoid valve as a function of a temperature error plus the
length of time the error exists.
A still further object of the invention is to vary the cycling rate
of a PWM solenoid valve to minimize temperature fluctuations during
periods of low heating demands by increasing the cycling rate, and
to minimize valve wear during periods of
Another object of the invention is to provide a constant,
non-varying airflow rate of variable temperature when heating and
to provide a variable airflow rate of a constant, non-varying
temperature when cooling.
Yet another object of the invention is to provide a VAV valve
assembly with an attached fan and check valve to assist in warming
a relatively cool supply airflow.
These and other objects of the invention are accomplished by a
novel VAV assembly. The assembly includes an airflow valve for
regulating the flow rate of a relatively cool supply airflow to be
delivered to a comfort zone. The assembly also includes a hot fluid
coil that, when needed, reheats the cool supply air. The average
flow rate of fluid through the coil is regulated by cycling the
valve open and closed in a PWM manner. When the temperature of the
zone is above its set point temperature, the solenoid valve remains
closed and the opening of the airflow valve is regulated to meet
the zone's cooling demand. When the temperature of the zone is
below its set point temperature, the solenoid valve is cycled with
a variable duty cycle to meet the zone's heating demand and the
airflow valve is controlled to provide a substantially constant
airflow rate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the subject invention used for temperature
conditioning a plurality of comfort zones.
FIG. 2 is a PWM signal controlling a solenoid valve with the signal
having a constant frequency.
FIG. 3 is a PWM signal controlling a solenoid valve with the signal
having a lower frequency at lower duty cycles.
FIG. 4 is a PWM signal controlling a solenoid valve with the signal
having a higher frequency at lower duty cycles.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, several comfort zones 10a, 10b, and 10c within
a building 12 are temperature conditioned by a refrigeration system
14. A refrigerant compressor 16, a condenser 18, an expansion
device 20, and an evaporator 22 are connected in series to comprise
a closed-loop refrigeration circuit 24. Evaporator 22 and an
evaporator fan 26 serve as a source of supply airflow 28 to zones
10a, 10b, and 10c. Evaporator 22 cools supply airflow 28 to a
temperature that is generally below the temperature of comfort
zones 10a, 10b, and 10c.
Supply airflow 28 is distributed to zones 10a, 10b, and 10c by way
of a supply air duct network means 30 comprising a plurality of
supply air ducts 32 connected to each zone. A return air duct
network 34 conveys air from these zones and returns it back to
evaporator fan 26 for recirculation through the system.
Each zone 10a, 10b, and 10c is associated with a VAV valve 36, 38,
and 40 that regulates the rate at which supply air 28 is delivered
each zone. Each VAV valve assembly 36, 38, and 40 includes a valve
body 42, 44, and 46 connected to a supply air duct 32.
Valves 36, 38, and 40 have several similar features so a
description of their operation will be made with reference only to
zone 10a and its associated VAV valve 36, keeping in mind that the
description applies to valves 38 and 40 as well.
VAV valve 36 includes a moveable closing member 48 disposed within
valve body 42. Closing member 48 is repositioned by a drive means
50. The variable positions of closing member 48 determines the flow
rate of supply airflow 28 passing through valve 36. Closing member
48 is schematically illustrated as a rotatable damper blade;
however, member 48 represents any device that can vary the flow
rate of air such as a plug valve of linear movement (e.g., the
valves of U.S. Pat. Nos. 4,749,000 and 4,749,001 specifically
incorporated by reference herein), a gate-type valve, or even an
inflatable bladder. Drive means 50 represents any device for
varying the position of member 48. Few examples of drive means 50
include motors, cylinders, and diaphragms.
Drive 50 modulates the position of VAV valve 36 under the control
of a command signal 52 provided by a microcomputer based control
means 54. Control means 54 relies on an internally stored algorithm
to generate command signal 52 in response to a temperature feedback
signal 56 and a flow rate feedback signal 58. The specific design
of control means 54 can vary widely, depending on the specific
input and output devices employed (items 50, 60, 62, and 66 which
are further explained below) It should also be appreciated that
microcomputer based control means 54 can be replaced entirely by
discrete electronic components.
The temperature feedback signal 56 is provided by a temperature
sensor 60 associated with the same zone 10a that is associated with
VAV valve 36. The temperature feedback signal 56 indicates the
error between a selectable desired set point temperature of zone
10a and the actual temperature of zone 10 a as measured by
temperature sensor 60. Flow rate feedback signal 58 is provided by
a flow sensor 62 which senses the flow rate of supply air 28
leaving VAV valve 36. Flow rate sensor means 62 represents any
device for sensing airflow, such as a Pitot tube. It should be
noted that in addition to or as an alternative, sensor 62 can be
connected upstream of VAV valve 36 (as is the case with valve 40)
to measure the rate of airflow entering valve 36.
When the temperature of zone 10a exceeds the set point temperature,
control 54 commands drive 50 to open valve 36 to an extent that
will provide an airflow rate which meets the cooling demand. The
desired rate of airflow, and thus the valve position, is a function
of the temperature error and the length of time the error exists
(e.g., porportional plus integral control). Control 54 uses flow
rate feedback signal 58 to ensure that the commanded valve position
actually results in the desired rate of airflow. If desired,
control 54 may further adjust the position of closing member 48 to
minimize the difference between the actual rate of airflow and the
desired rate of airflow. The position of closing member 48 is
adjusted to reduce the error between the zone temperature and its
set point.
If the temperature of zone 10a drops below a set point temperature,
valve 36 is still held partially open to provide at least some
airflow 28 for adequate ventilation. However, to prevent zone 10a
from getting uncomfortably cold, a heating coil 64 is employed
within valve body 42. Coil 64 conveys a heated fluid, such as water
and/or glycol, that is sufficiently warm to heat airflow 28 to a
temperature greater than that of comfort zone 10a.
The extent to which airflow 28 is heated by coil 64 is controlled
by a solenoid valve 66 connected in series with heating coil 64.
Solenoid valve 66 is cycled open and closed in a pulse-width
modulated manner to meet the heating demand of the comfort zone.
The cycling of solenoid valve 66 is controlled by a command signal
68 generated by control 54 in response to the zone temperature
error and, if desired, in further response to the length of time
that the error exists.
Referring to FIG. 2, in one embodiment of the invention, solenoid
valve 66 is cycled at a relatively constant frequency with a
variable open-period 70 within each cycle 72. FIG. 2 illustrates a
cycle period 72 of three minutes, or in other words, the frequency
is once every three minutes. The percentage of open-period 70
within each cycle period 72 is referred to as duty cycle. The duty
cycle increases with the heating demand. Region 74 represents a 90
% duty cycle to meet a relatively high heating demand. With a 90 %
duty cycle, valve 36 has an open-period 70 of 162 seconds and a
closed-period 76 of 18 seconds during a total cycle period 72 of
three minutes. Region 80 represents a 20 % duty cycle to meet a
relatively low heating demand, and Region 78 represents a 50 % duty
cycle.
While coil 64 is being used to reheat airflow 28, closing member 48
of VAV valve 36 is positioned to provide a relatively constant flow
rate to satisfy minimum ventilation requirements. This can be
accomplished by generally holding closing member 48 at (or just
below) a fixed predetermined position. For greater control, the
position of closing member 48 can be modulated in response to the
flow rate feedback signal 58 to ensure a constant flow rate.
In another embodiment of the invention, referring to FIG. 3, the
duty cycle is varied to meet the demand by maintaining a constant
open-period 70 while varying cycle period 72. Open-period 70 is set
to allow sufficient time for a complete exchange of fluid within
coil 64. Region 82 represents a 90 % duty cycle, region 84
represents a 50 % duty cycle, and region 86 represents an 80 % duty
cycle.
In yet another embodiment of the invention, referring to FIG. 4,
the frequencies vary to limit closed-period 76 to less than a
predetermined maximum. Excessively long closed-period 76 between
open-period 70 can cause uncomfortable temperature fluctuations of
airflow 28. These fluctuations are minimized by increasing the
cycle frequency at lower duty cycles, such as in region 88 where
the duty cycle is 10 %. Region 90 represents a duty cycle of 50 %,
and region 92 represents a duty cycle of 80 %.
Referring back to FIG. 1, to conserve energy in meeting a heating
demand fan means 94 or 96 and check valve means 98 can be added to
VAV valve assemblies 36, 38, and/or 40, check valve means 98
represents any device that provides greater flow resistance in one
direction than n an opposite direction. Ideally, the flow will be
substantially blocked in one direction and relatively unrestricted
in the other direction. Fan means 94 and 96 represent any device
for delivering kinetic energy to air such as an axial or
centrifugal fan. Fan 94 is mounted outside of valve body 44 and
discharges ambient air 100 into it. As an alternative, fan means 96
is disposed entirely within valve body 46 and draws ambient air 100
into valve body 46. Ambient air 100, as referred to herein, is the
air surrounding any valve body 42, 44, or 46. Valve bodies 42, 44,
and 46 and the surrounding ambient air 100 are generally above a
ceiling 102 of a comfort zone where the air temperature is
generally higher than that of the comfort zone. Thus the relatively
warm ambient air 100 can assist in warming an uncomfortably cool
comfort zone. Check valve means 98 is located downstream of closing
member 48 and prevents cooled supply air 28 from discharging into
ambient air 100. With internally mounted fan means 96, check valve
means 98 can be eliminated by operating fan 96 at a sufficiently
high speed that would ensure that the air pressure between closing
member 48 and fan 96 is less than the ambient air pressure.
Although the invention is described with respect to a preferred
embodiment, modifications thereto will be apparent to those skilled
in the art. Therefore, the scope of the invention is to be
determined by reference to the claims which follow.
* * * * *